1. Field of the Invention
The present invention relates to a speed change control apparatus of an automatic transmission capable of selecting between an auto-mode performing a speed change on the basis of a running condition and a manual mode performing a speed change on the basis of a manual manipulation.
2. Description of Related Art
As conventional speed change control apparatuses of an automatic transmission, there is one, for example, disclosed in Japanese Patent Laid Open Publication Hei No. 2-8545.
This conventional apparatus is constructed, on the basis of a shift apparatus provided in a normal automatic transmission, a manual shift function including a plus sensor outputting an up-shift signal and a minus sensor outputting a down-shift signal is added to operate such that a shift lever is moved from a "D" range position which selects a normal running to a manual shift position, and here, a speed change stage of the transmission is shifted up by one speed to a higher speed side by operating the plus sensor, conversely, the speed change stage is shifted down by one speed by operating the minus sensor.
In the conventional speed change control apparatus of an automatic transmission mentioned above, it is advantageous in that under a running condition in the auto-mode by selecting the "D" range, it is possible to perform the up-shift and the down-shift by switching to the manual mode so that the speed change stage can be selected in accordance with a preference of a driver. However, an unsolved problem is involved in that there is a fear of causing an overspeed condition of the engine due to the down-shift by the manual manipulation.
In order to solve this unsolved problem, it is considered as disclosed, for example, in Japanese Utility Model Laid Open Publication No. 61-169629, to inhibit the down-shift speed change and to hold the gear position there by to prevent the overspeed of the engine regardless of the normal judgement that the down-shift should be performed, when it is predicted that the engine will be in the overspeed condition if the down-shift speed change is attempted.
However, in this case, as shown in FIG. 7, assuming that a speed change line L.sub.1 is set for changing from the fourth speed to the third speed established on the basis of a vehicle speed V and a throttle opening degree TH during manual speed change, and a speed change line L.sub.2 is set for changing from the third speed to the second speed, the speed change process is dealt with in the same way when a vehicle speed V.sub.A at the time of the down-shift request is close to the speed change line L.sub.1, and when a vehicle speed V.sub.B at the time of the down-shift request is far from the speed change line L.sub.1.
More specifically, when a minous sensor is operated at the vehicle speed V.sub.A, since the engine speed at the down-shift which is calculated at this time will be exceeding the overspeed, the operation of the minous sensor is neglected, and the down-shift operation is performed for the first time by manipulating the minous sensor when the vehicle speed V reaches a vehicle speed of the speed change line L.sub.1 or lower. Also, when the minous sensor is operated at the vehicle speed V.sub.B since the engine speed at the time of down-shift which is calculated at this time will be exceeding the overspeed, the operation of the minous sensor is neglected, and the down-shift operation is performed for the first time when the minous sensor is manipulated when the vehicle speed V reaches the vehicle speed of the speed change line L.sub.1 or lower. Thus, a new problem is involved in that, in either case, it is the same that the down-shift request is neglected, and even in the case where the minous sensor is operated at the vehicle speed V.sub.A, and for example, after 0.5 seconds, the vehicle speed reaches the vehicle speed of the speed change line L.sub.1 or lower, the shift request is neglected and the driver cannot achieve his intended running condition.